The invention relates to a hip prosthesis and a method for fitting such hip prosthesis.
Examples or a known hip prosthesis and a known method for fitting such hip prosthesis are for instance described in EP-A-0 145 339. In general, such so-called total hip joint prostheses comprise two parts: a femoral head prosthesis and an acetabular prosthesis.
The known femoral head prosthesis comprises a head in the form of a hemisphere and a stein extending from the head and suitable for being secured in the medullar canal of the femur. The acetabular prosthesis comprises a hemispherical cup fixed in the acetabulum of the hip bone by means of cement, screws or the like.
A major drawback of the known hip prostheses is formed by the manner in which these hip prostheses should be fitted. This fitting involves a very difficult operation taking up a number of hours. In particular in the case of older patients, the operation is not without risks. Moreover, essential tissues, such as the joint capsula and the ligaments, are cut through, which results in a decreased stability of the joint and a long recovery period. In addition, complications may occur in the form of infections, loosening of the femoral prosthesis from the medullary canal, fractures and inflammation of the joint capsula caused by splinters or parts coming from the acetabular prosthesis. Moreover, the reaming of the medullary canal in the femur may have harmful effects, such as, for instance, micro-embolisms. The hip prostheses known from SU-A-749 392, GB-A-2 250 919 and WO-A-89 11 837 are also mounted during major operations in which the above mentioned essential tissues have to be cut through resulting in a decreased stability of the joint and a long recovery period.
The object of the invention is to provide a hip prosthesis and a method for fitting such a hip prosthesis wherein the above-described drawbacks do not occur, or at least to a smaller extent.
To this end, in accordance with the invention, the hip prosthesis comprises a first fastening assembly intended for being mounted in the hip bone and a second fastening assembly intended for being mounted in the upper extremity of the femur, wherein the first and the second fastening assembly are interconnected by means of a pivotable connection, wherein all parts of the hip prosthesis are so small and/or slender that they can each be arranged in the intended end position thereof via a bore in the femur, which bore extends from the outside of the femur through the femoral neck substantially in the direction of the imaginary longitudinal center line of the femoral neck to the femoral head.
The invention also provides a method for fitting such a hip prosthesis, wherein a small incision is made in the leg to gain access to the top part of the femur, wherein a femoral bore is subsequently made in the femur, which femoral bore extends from the outside of the femur through the femoral neck substantially in the direction of the imaginary longitudinal center line of the femoral neck to the femoral head, wherein the femoral head is subsequently removed via the femoral bore, wherein, via the femoral bore, a hip bone bore is subsequently made in the hip bone at the location of the acetabulum, wherein, via the femoral bore, the first fastening assembly is subsequently mounted in the hip bone bore and the second fastening assembly is mounted in the femoral bore, after which, finally, the incision is closed.
The hip prosthesis and the method for fitting the hip prosthesis are particularly advantageous especially because the operation is far less drastic, owing the construction of the hip prosthesis. The total replacement of the hip joint can be carried out intraluminally, i.e. via the bore in the femur. Optionally, such an operation can be carried out under local anaesthesia in an outpatients"" department. At any rate, the patient""s residence in the hospital can be shortened considerably, Moreover, the danger of infection is reduced considerably. A very important advantage is that the muscles, the Joint capsula and the ligaments around the joint remain untouched during the fitting of the hip prosthesis according to the invention. Further the amount of bone which has to be removed is kept minimal. A further advantage is that revision of the prosthesis or parts thereof is feasible. This was impossible during the implantation or fitting of the known prostheses, which inter alia had the result that the recovery period after the fitting of the known prosthesis was fairly long and, moreover, an extensive follow-up treatment with excercises was necessary. When fitting the hip prosthesis according to the invention utilizing the method according to the invention, damage to the tissues around the hip joint is minimized.
It is observed that U.S. Pat. No. 4,714,478 discloses a hip prosthesis which can also be fitted via a bore in the femur without damaging the joint capsula, the surrounding muscles and ligaments. However, this does not concern a so-called total hip prosthesis but only a replacement of the Femoral head. Hence, this known solution cannot be used in patients whose acetabulum is damaged. Another drawback of the known apparatus is that the femoral head prosthesis is manufactured from flexible, compressible material that can be filled with, for instance, a hardening plastic after having been brought into the desired position. During this filling, the prosthesis part positioned at the location of the original femoral head assumes the shape of a femoral head. However, a drawback is that each femoral head has a different radius and shape, so that each prosthesis should be specifically manufactured for a patient in question. This type of made-to-measure work is very costly. Moreover, it is not easy fo find materials that are on the one hand sufficiently flexible so as to be able to be folded together, and on the other hand sufficiently resistant to wear so as to be able to serve as joint surface.